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Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
51 lines
1.5 KiB
Plaintext
51 lines
1.5 KiB
Plaintext
; feed/page — pagination. Offset/limit for indexed access, and cursor-based
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; (by :at) for recency feeds, which is stable under inserts: a cursor is the
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; :at of the last item seen, and the next page is the newest items older than it.
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;
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; Requires: lib/feed/stream.sx (feed/recent, feed/take, feed/filter).
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; --- offset / limit ---------------------------------------------------------
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(define
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feed/page
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(fn
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(stream offset limit)
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(feed/stream (take (drop (feed/items stream) offset) limit))))
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(define
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feed/page-count
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(fn (stream limit) (ceil (/ (feed/count stream) limit))))
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; --- cursor (recency feeds) -------------------------------------------------
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; activities strictly older than cursor (scroll down / load older)
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(define
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feed/before
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(fn
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(stream cursor)
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(feed/filter stream (fn (a) (< (get a :at) cursor)))))
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; activities strictly newer than cursor (load newer / "N new posts")
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(define
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feed/after
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(fn
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(stream cursor)
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(feed/filter stream (fn (a) (> (get a :at) cursor)))))
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; one page: the `limit` newest activities older than cursor, newest first
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(define
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feed/page-before
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(fn
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(stream cursor limit)
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(feed/take (feed/recent (feed/before stream cursor)) limit)))
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; cursor to fetch the next (older) page: :at of the last item of a page,
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; or nil when the page is empty (end of feed)
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(define
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feed/next-cursor
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(fn
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(page)
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(let
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((items (feed/items page)))
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(if (= (len items) 0) nil (get (last items) :at)))))
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